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1

Comparison of the Vibration Response of a Rotary Dobby with Cam-Link and Cam-Slider Modulators

Yu Hongbin, Yin Honghuan, Peng Junqiang, Wang Lei

Autex Research Journal

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2021

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Vol. 21, no. 4

491--500

EN

This article presents the kinematic modeling and analysis of cam profiles of two different types of modulator: a cam-link and a cam-slider modulators. Kinematic and dynamic models of the two different modulators were established based on the motion curves of the main shaft of the rotary dobby. Simulations were carried out in Simulink to analyze the vibration responses under different rotary speeds, and vibration responses of the two mechanisms were compared. The results show that the cam-link modulator vibrates smoothly at speeds of <700 rpm, and theoretically, the speed should not exceed 1,400 rpm. The cam-slider modulator vibrates smoothly at speeds of <500 rpm, and theoretically, the speed should not exceed 1,000 rpm. The cam-slider modulator is more suitable for use at low speeds, whereas the cam-link modulator is more appropriate for high speeds. When both the cam-slider and cam-link modulators operate at high speeds, vibration distortion occurs, leading to bifurcation and chaotic vibration. Further knowledge of the complex behaviors associated with detachment of the follower from the cam can support the design of more sophisticated controllers aimed at avoiding follower detachment.

2

Assessing and controlling of boulder deep-hole blasting-induced vibrations to minimize impacts to a neighboring metro shaft

Zhang Zhiqiang, Li Yonglong, Wang Shuo, Zhang Heng, Qian Yang

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 2

421--440

EN

When a metro is constructed by the shield method in the strata containing boulder group, it is prone to some engineering problems such as serious cutter wear, deformation of the cutter holder head, damage of the cutter spindle, which seriously affects the construction efficiency and bring enormous problems to the shield construction. This paper proposes the vibration reduction measures for the boulder deep-hole blasting to meet the construction safety. To achieve this purpose, the field test was applied to investigate the vibration response of adjacent building under five blasting areas. Then, three-dimensional numerical model was employed to discuss the vibration characteristics of the boulder and adjacent buildings under vibration reduction measures. The results show that increasing the damping hole and the isolation hole and changing the charging layout of the blasting areas can blast the boulder under the condition of ensuring effective and safe construction. Damping hole and isolation hole have a positive role in the control and attenuation of blasting stress wave. All of them have good vibration reduction effect, and the vibration reduction efficiency is more than 90%. The double row damping holes with 12.7 cm diameter and 20 cm spacing have good vibration reduction effect and economic benefit. When double row damping holes are used, the maximum particle velocity of the shaft structure under the influence of blasting stress wave is 1.47 cm/s, which is within the reasonable safety range.

3

The steam pressure impacts reducing system for a biomass cogenerator based on monitoring of the frequency characteristics of the steam actuator

Lalik Krzysztof, Podlasek Szymon, Goryl Wojciech, Góra Grzegorz

Vibrations in Physical Systems

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2019

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Vol. 30, nr 2

art. no. 2019224

EN

Introduced through policy instruments, as well as due to increase awareness of and demand for energy, alternative, renewable energy sources are becoming increasingly popular and necessary. The growing market and standards are forcing producers of renewable energy sources to constantly improve the quality of their products. Biomass trigenerators are one way of obtaining such energy, both in the form of electricity, heat and cold. These are elements generating steam by burning various solid, liquid or gaseous fuels of organic origin. Rotating machines in the form of turbines or steam engines are used to generate electricity. Unfortunately, they are particularly exposed to steam impacts associated with discontinuous work. This article presents the monitoring and prevention system for such impacts. It is based on the analysis of the frequency spectrum of vibrations of such generators and can be used to implement a trigenerator control system that will reduce the influence of such impacts. With proposed diagnostic system, the efficiency and life span of a Renewable Energy Source can increase significantly.

4

Effect of the multiple damages and temperature changes on the natural frequency

Mohammadi Esfarjani S., Salehi M., Ghassemi A.

Journal of Theoretical and Applied Mechanics

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2017

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Vol. 55 nr 3

813—822

EN

Damage detection based on structural dynamic characteristics, such as natural frequencies and mode shapes, is an important area of research. Obtaining accurate structural dynamic characteristics is perhaps the most challenging aspect. In particular, changes in environmental temperature due to seasonal weather or radiation from sunshine leads to changes in the dynamic characteristics of structures. An important conclusion is that changes in the dynamic characteristics of a structure due to damage may be smaller than changes in the dynamic characteristics due to variations in temperature. Also, damage can affect the frequency response. This is the first study of evaluation of the effect of changes in temperature and multiple damages on natural frequency at the same time. In this paper, the simultaneous effect of the multiple defects and temperature on the natural frequencies of 6063 aluminum alloy beam are assessed numerically. ABAQUS finite element software is used for the numerical analysis. The present paper aims to evaluate the temperature effect and multiple damages on vibration responses. The variations in the frequency have been analysed in simulation by using an aluminum specimen and obtaining impedance signatures at temperatures ranging from −200◦C to 204◦C. The results show that an increase in temperature leads to a decrease in structural frequency, and that a decrease in temperature leads to an increase in structural frequency. The evaluation of the effect of multiple defects on natural frequency shows that when damages are created in the structure, there is a significant decrease in the natural frequency responses of the 6063 aluminum alloy beam. The results show that damage causes a decrease in the natural frequency of the structure. This study highlights the importance of applying simulation methods to the evaluation of the effect of changes in environmental temperature and multiple damages on the dynamic characteristics such as natural frequencies and mode shapes, especially at the same time.